Information storage display tube and storage screen assembly therefor



ORAGE DISPLAY TUBE AND STORAGE SCREEN ASSEMBLY THEREF'OR Filed Dec. 18, 1957 `duce the resolution of the resulting display image.

Unite States 3,031,597 INFORMATION ASTORAGE DISPLAY TUBE AND STORAGE SCREEN ASSEMBLY THEREFOR Dean W. Davis, Fort Wayne, Ind., assigner to International Telephone and Telegraph Corporation Filed Dec. 18, 1957, Ser. No. '703,659

Claims. (Cl. 315-12) Vcent viewing screen disposed at the other end. A storage screen assembly is conventionally positioned within the envelope intermediate the electron guns and lthe viewing `screen andhas conventionally been formed of a sheet ofV dielectric material having a plurality of openings formed therethrough with a line screen in contact with or coated on the side of the dielectric sheet, the dielectric material of the storage screen assembly being positioned toward the electron guns. A tine-mesh metal collector screen is also conventionally positioned within the envelope in front of the storage screen, ,i.e., on the side thereof toward thejelectron guns. During fwriting, the pencilj beam is caused to scan the storage screen, the beam commonly being modulated by applying an input signal to a control grid of the high velocity electron gun. Impingement of Vthe high velocity electron beam upon the dielectric'surface of the storage screen assembly causes the emission -of secondary electrons which are collected by the collector screen and thus elemental charges areformed on the ie cric sur ace o t e s orage screen ro or iona o `d let f f h t t lt Vdielectric surface thereby causing an image to `appear on the display screen in accordance with the charge pattern on the storage screen. t

In prior storage screen assemblies known to the applicant, with a metal screen in contact with the back surface of the dielectric sheet only, i.e. the surface toward the display screen, an elemental charge on the dielectric sheet in the region of one opening therein could controlV` the flood electrons in adjacent openings, thus tending to re- Furthermore, with priorfstorage screen assemblies, the poten- `tial gradients within each opening tended to focus the flood electrons in front of the display screen again reducing the resolution of the display image.

I have found that-by providing a second metal screen in contactl With or coated on the front surface of the dielectric sheet, i.e. the side towad the electron gun, with the openings in the second metal screen being respectively in registry with and slightly larger than the openings in the dielectric sheet thereby exposing a portion of the front surface of the dielectric sheet around each opening therein, the web portions of the second metal screen effectively isolate each opening in the dielectric sheet and its surrounding marginal peripheral dielectric surface from every other opening so that the elemental charge surrounding each opening cannot control the ow of flood Y electrons through adjacent screen openings, thereby imy proving the resolution of the display image. Furthermore,

ate .t

applied to the front and back metal screens, each opening vcan be made lto function as an electron optical lens with .an adjustable focal length so that the flood electrons passing through the storage screen openings can be focused With their point of convergence `at or near the display screen thereby still further improving the resolution of the resulting display image. Furthermore, with my improved storage 'screen assembly, I4 have found that the provision of the additional front metal screen permits the application of a negative potential to the back screen and pulsing the front screen positive during the erasing operation thereby obtaining a faster erasing action. In addition, by the provision of the additional front screen, it is possible to eliminate the separate collector screen with the front screen assuming its Vfunction thereby preventing re-distribution of secondary electrons, eliminating writing beam dispersion between the collector and insulator, permitting optimum utilization of current, and providing better uniformity of the field at the dielectric surface. The provision of my improved storage screen assembly therefore results in a greatly improved storage tube having a brighter display image With higher resolution, faster writing and erasing speed, and better uniformity.

It is accordingly the object of my invention to provide t an improved storage screen assembly for charge storage Y tion of the displayed image'.

A still further object of my invention is the provision of an improved charge storage tube of the display type incorporating anV improvedv storage screen assembly with cooperating means for improving the resolution of the displayed image.

Yet another object of this invention is the provision of a charge storage tube incorporating my improved storage screen assembly with cooperating means for increasingthe erasing speed.

A A further object of my invention is the provision of a charge storage tube incorporating an improved storage screen assembly which permits elimination of the separate collector screen provided in prior charge storage tubes.

' The above-mentioned and other features and objects V`of this invention and the manner of attaining them will become more iapparent Vand the invention itself will be best understood'by reference to the following description Vof an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

- FIG. l is a cross-sectional view of a signal-to-image charge storage tube incorporating my improved storage s creen assembly. l

FlG. 2 is a. fragmentarycross-sectional view illustrating my improved storage screen assembly and its oodrbeam focusing action; and

FIG. 3 is a fragmentary front view of my improved storage screen assembly taken along the line 3 3 of FIG. 2.

Referring now to the drawing, there is shown a signal-l toimage display tube, generally identified asl, which comprises an enclosing envelope 2, conventionally formed of glass. An electron gun assembly 3, of any convenfactory.

tional design, is positioned on the axial center line of the envelope 2 and provides a low velocity ood electron beam for reading-out the stored signal. Another electron gun assembly d, also of conventional design, is provided offset from the low velocity gun 3 for providing a high velocity pencil beam for writing the information upon storage screen assembly 5. The pencil beam provided by high velocity electron gun 4 is caused to scan the front surface of storage screen assembly 5 by conventional focusing and deflecting elements (not shown). A luminescent viewing screen 6 is formed at the end 7 of envelope 2 remote from the electron guns 3 and 4. The inner surface of the envelope 2 intermediate the guns 3 and 4 and the storage screen assembly 5 is conventionally coated with a conductive coating 8 as is common in the art. A tine-mesh metal collector screen 9 is positioned within the envelope 2 closely spaced from the storage screen assembly S on the side thereof toward the electron guns 3 and 4. v

ReferringV now more particularly to FIG. 2, my improved storage screen assembly 5 includes a relatively thin sheet 10 of dielectric material, such as glass, having a plurality of geometrically arranged, Iclosely spaced, relatively small openings 11 formed therethrough. The openings 11 are tapered, as at 12, so that the openings 13 on the back side 14 of the dielectric sheet 10 are larger than the openings on the front side 16 of the dielectric sheet 10.

The dielectric sheet 10 is preferably, but not necessarily, formed of fotoceram with the openings 11 suitably etched therethrough. lFotoform glass is a recently developed glass product which has a photo-sensitive material therein and which may be etched in a ratio of 5 to 1. Thus, a fine-mesh screen mask may be laid on a fotoform glass plate approximately tive mils thick and exposed to ultraviolet light; the portions of the plate which have been exposed to the ultraviolet light may then be etched with suitable acid, the exposed areas etching five times faster than the unexposed areas. In this manner, the openings or holes 11 may be etched entirely through the sheet or plate 10, and the front and back surfaces or sides 14 and 16 then ground smooth to obtain a plate on the order of three mils thick. The plate is then baked, which results in a further change in the properties thereof to provide greatly increased resistivity, the resulting disc or wafer which may, for example, be two inches in diameter, three mils thick with the openings 11 defining as high as a 500 mesh screen being referred to as fotoceram. It is to be understood that the above described method of etching a fine-mesh screen in a thin glass plate is not the subject of this invention and it is possible that other means may be found for providing a plurality of geometrically arranged, closely spaced small openings in a dielectric sheet. The etching of the fotoform glass sheet is performed on the back surface or side 14, thus providing the taper 12 in the openings 11, it having been found that a taper of approximately 10 degrees is satis- It is desirable to provide this taper, so that the smaller openings 15 face toward the electron guns 3 and 4, and the larger openings 13 face toward the display screen 6, in lorder to prevent the low velocity flood beam from the electron gun 3 from striking the walls of the openings 111 and thus providing an unwanted charge pattern on the storage screen assembly.

Storage screens incorporating a fotoceram dielectric layer with etched openings formed therein have been provided in prior charge storage tubes. In such tubes it has been common practice to evaporate a thin layer of metal, such as aluminum onto the web portions 17 surrounding the openings 13 in the back side of surface 14 of the dielectric sheet 10 thereby to provide a relatively thin metal screen 18 on the back side 14 of dielectric sheet 10 with its openings in registry with the openings 11 in the dielectric sheet 10 and substantially coextensive therewith.

In accordance with my invention, I provide a second relatively thin metal screen 19 contacting the web portions 20 surrounding the front openings 15 in the front side 16 of the dielectric sheet 10, the screen 19 having its openings 21 respectively in registry with but substantially larger than the openings 15 thereby exposing a portion 22 of the front surface 16 of the dielectric sheet 10 surrounding each of the front openings 15. This metal front screen 19 may be evaporated onto the front side or surface 16 of the dielectric sheet 10 in the same manner as the metal back screen 18 and etched with acid to expose the dielectric front surface 16.

Referring now again particularly to FIG. 2, in prior charge storage tubes having only the back metal screen 18, without the additional front metal screen 19, the back metal screen 18 was conventionally connected to a slightly positive source of potential 33, such as plus 20 volts, by lead 23. The whole frontsurface 16 of the dielectric sheet 10 during the reading operationis at a potential of zero volts or even slightly minus; it cannot have a potential higher than zero because it is being struck by the flooding electrons as shown by the dashed lines 23. Thus, with the back screen 13 at a slightly positive potential and the front surface 16 of the dielectric sheet 10 either Zero or slightly minus, equipotential lines having a configuration shown by the dashed lines 24 were formed which tended to cause the flood electron streams 23 to bend and cross over, as at 25, the ood electron streams diverging after the point 25, as at 26, thus adversely affecting the resolution of the resulting display image on the display screen 6.

With my improved storage screen assembly 5 having the metal front screen 19, the frontscreen 19 may be connected to a suitable source of potental 34, by lead 27 so that the equipotential lines in the front openings 15 form a divergent electron lens which may be adjusted in essence to cause the low velocity flood electrons entering openings I15 to diverge. The net focusing action of the divergent electron lens in the openings 15 and the convergent electron lens in the openings 11 therefore can be made dependent upon the relative potential gradient of the back screen 18 and the front screen 19 with respect to the exposed portion 22 of the front surface 16 so that the point of convergence of the ood electron streams can be moved outwardly to the display screen 6, as at 29 so that the resolution of the resulting display image is improved. It is thus seen that byfapplying appropriate potentials on the front and back screens 18 and 19 respectively by means of leads 23 and 27, each opening 11 in the dielectric sheet 10 with its corresponding openings in the front and back metal screens in essence forms an electron lens which permits focusing of the image on the display screen 6 during the reading operation to obtain optimum resolution. In a typical signal-to-image storage tube, both the front and back metal screens 18 and 19 may, for example, have 20 volts positive applied thereon with a potential of plus volts being applied to the collector screen 9 from source 35 by a lead 29, a potential of plus 7,000 yvolts applied on the display screen 6 from source 36 by lead 30, and a potential of 25 Volts being applied on the accelerating anode 8 from source 37 by lead 31. It is thus seen that by raising the average potential just in front of the front openings 15 on the front side 16 of the dielectric sheet 10, the flood beam can be properly focused to improve the resolution of the resulting display image.

It will further be seen that in prior charge storage tubes which did not incorporate the front metal screen 19, the incremental charges on the front surface 16 of the dielectric sheet 10 produced by the modulated writing beam will control or at least effect flood electrons during the flooding operation, not only in the immediate opening 1v1, but also in adjacent openings. =In my improved storage screen assembly, the front screen 19 acts as a separator between the front charge storage elements of Vspense? the dielectric sheet the writing beam electrons which strike the metal web portions 32 of the front screen 19 do not charge any portion of the dielectric sheet and only the areas Z2 surrounding each front opening I15 are charged. Thus, during the reading operation, the incremental charges on each area 22 surrounding a particular front opening 15 will affect or modulate the flood electrons passing through that opening only and will not affect the ood electrons passing through adjacent openings.

-It will be seen that the additional front screen 19 has little effect on the primary writing beam during the writing operation since the writing beam provided by the writing electron gun 4 has high velocity. However, without the front screen 19, some of the secondary electrons emitted from the front surface 16 of the dielectric sheet 10 due to impingement of the writing beam thereon tend to migrate to an adjacent front surface rather than to the collector screen, such action being referred to as redistribution of secondary electnons. This redistribution of secondary electrons tends to erase incremental charge elements which have just been written on adjacent dielectric arcas, thus lowering the contrast of the ultimate display image. The additional front screen 19 of my invention collects these random secondary electnons or directs them away from the front surface -16 so that they do not charge adjacent dielectric areas. g

It will now be seen that my improved storage screen assembly with the provision of the additional front screen 19 may permit the complete elimination of the collector screen 9 with the front screen `19 having a suitable positive potential, applied thereon by leadI 27 at the proper level to secure the above-mentioned focusing action during the reading operation, and with appropriate voltages applied to the gun 3 and electrode 8 to collimate the flooding beam.

In prior display type signal-to-image tubes known to the applicant, in order to erase the stored image from the storage screen, a positive pulse was applied to the back screen which raised the potential of the front surface so Y that the ood electrons in striking the front surface would charge the front surface negative. Thus in such prior devices, the ood electrons passing through the openings in the storage screen during erasing served no useful purpose but undesirably reduced the contrast of the display. With my improved storage screen assembly, the back screen 18 can be made negative, such as at -10 volts by connection to source 38 by a switch 39 so that the flood electrons will not pass through the openings 111 and the front screen 19 can be pulsed, with, for example, plus 40 volts lby connection to source 40 by a switch 41, thus raising the potential of the front surface of the dielectric sheet 10 so that a larger amount of flood electrons strike the front insulator surface 22 surrounding the front openings 15 of the dielectric sheet `10, thus providing faster erasing action.

When the collector screen 9 only is provided in front of the storage screen assembly, the potential of the front surface 16 of the dielectric sheet 16 is substantially lower than that of the collector 9, and there is a decelerating elfect as the flood electrons approach the dielectric sheet 10, and some of the flood electrons will be deected and repelled at a distance substantially before the plane of the front surface 16 and will return to the collector screen 9. By eliminating the collector screen 9 and utilizing the front screen 19 as the collector screen, the collector screen has in essence been moved directly up to the front surface 16 of the dielectric sheet 10 and thus the velocity of the flood` electrons is maintained relatively high up to the very sur-face of the dielectric sheet 10 so that they are not so easily deflected. Thus with my. improved storage screen assembly which permits complete elimination of a separate collector screen, turning back of ood electrons is eectively prevented, thus more ood electrons pass through the openings in the screen and produce a brighter display image on the screen 6.

' It Will now be seenv that my improved storage screen withthe front metal screen 19 makes possible the provision of an improved display type storage tube since it permits focusing of the image section of the tube, thus improving resolution. It additionally improves resolution by reducing overlap of incremental charge areas'on the :front surface of the storage insulator. My improved storage screen assembly further reduces the size of the incremental storage elements, makes possible faster erasing by permitting positive pulsing of the front surface of the dielectric sheet, and also prevents redistribution of secondary electrons. My improved storage screen assembly further may make possible the complete elimination of the collector screen with the front metal screen taking over the collector screen functions, thus eliminating flood beam dispersion between the collector screen and the dielectric sheet, and permitting maximum utilization of the flood beam electrons. It is thus seen that charge storage tubes incorporating my improved storage screen assembly will provide a brighter display imagehaving higher'resolution, and such tubes will have faster Writing and erasing speed and better uniformity..

While, my improved storage screen assembly has been .illustrated and described in connection with a signal-to image display tube, it will be readily apparent that it is equally applicable to an image-to-irnage display tube.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to' the scope of my invention.

What is claimed is:

'1. A storage display screen assembly for charge stofage tubes comprising: a relatively thin self-suppcrtingat sheet of dielectric'material having a plurality of relatively small uniformly tapered openings formed therethrough so that the openings on one side of said sheet are larger than the openings on the other side of said sheet; a relatively thin flat metal screen in contact with and supported by said one side of said sheet and having its openings respectively in registry and substantially coextensive with said larger sheet openings; and another relatively thin flat metal screen in contact with and supported by the other side of said sheet andrhaving its openings respectively in registry with and larger than said smalier sheet openings thereby exposing a portion of said other side of said sheet around each of said smaller sheet openings.

2. In a display-type charge storage tube, flood electron beam source means disposed at one end of said tube and a viewing screen disposed at the other end thereof, and a storage screen assembly comprising: a relatively thin sheet of dielectric material having a plurality of relatively small openings formed therethrough; a first relatively thin metal screen in contact with one side of said sheet and having its openings respectively in registry with said sheet openings; and a second relatively thin metal screen in contact with the other side ofsaid sheet and having its openings respectively in registry with and larger than said sheet openings thereby exposing a portion of said other side of said sheet around each ofisaid sheet openings; said storage screen assembly being disposed with said second metal screen facing said electron beam source means; and means for impressing approximately equal positive potentials on both of said screens to form electron lenses for focusing said flood electron beam onto said display screen.V

3. In a display-type charge storage tube, flood electron beam source means disposed at one Vend of said tube and a viewing screen disposed at the other end thereof, and a storage screen .assembly comprising: a relatively thin sheet of dielectric material having a plurality of relatively small openings formed therethrough; a first relatively thin metal screen in contact with one side of said sheet and having its openings respectively in registry with said sheet openings; and a second relatively thin metal screen in contact with the other side of said sheet and having its openings respectively in registry with and larger than said sheet openings thereby exposing a portion of said other side of said sheet around each of said sheet openings; said storage screen assembly being disposed with said second metal screen facing said electron beam source means; and means for impressing a negative potential on said tirst screen and a positive potential on said second screen for erasing the information stored on said storage screen assembly.

4. In a display-type charge storage tube, flood electron beam source means disposed at one end of said tube and a viewing screen disposed at the other end thereof, and a storage screen assembly comprising: a relatively thin sheet of dielectric material having a plurality of relatively small openings formed therethrough; a rst relatively thin metal screen in contact with one side of said sheet and having its openings respectively in registry with said sheet openings; and a second relatively thin metal screen in contact with the other side of said sheet and having its openings respectively in registry with and larger than said sheet openings thereby exposing a portion lof said other side of said sheet around each of said sheet openings; said storage screen assembly being disposed with said second metal screen facing said electron beam source means; means for at times impressing approximately equal positive potentials on both of said screens to form electron lenses for focusing said ood electrons onto said display screen during reading of the information stored on said storage screen assembly; and means for at other times impressing a negative potential on said first screen and a positive potential pulse on said second screen for erasing the information stored in said storage screen assembly.

5. ln a displayetype charge storage tube, a high velocity writing electron beam source and a low velocity flood electron beam source disposed at one end of said tube and a viewing screen disposed at the other end thereof, and a storage screen assembly comprising: a relatively thin self-supporting flat sheet of dielectric material having a plurality of geometrically arranged closely spaced unitormly tapered openings formed therethrough so that the openings on one side of said sheet are larger than the openings on the other side of said sheet; a relatively thin layer of metal deposited on the web portions of said one side of said sheet to form a first metal screen having its. openings respectively in registry and substantially coextensive with said larger sheet openings; a relatively thin layer of metal deposited on the web portions of said other side of said sheet to form a second metal screen having its openings respectively in registry with and larger than said smaller sheet openings; said storage screen assembly being disposed between said electron beam source and said viewing screen with said second metal screen facing toward said electron beam source; and means for impressing approximately equal positive potentials on said metal screens during operation of said ood electron beam source so that each of said sheet openings and its respective screen openings form a compound electron lens for focusing said flood electron beam onto said viewing screen.

References Cited in the tile of this patent UNITED STATES PATENTS 2,118,186 Farnsworth May 24, 1938 2,240,186 Iams Apr. 29, 1941 2,259,506 Young et al. Oct. 21, 1941 2,507,958 Cassman May 1.1, 1950 2,790,929 Herman et al Apr. 30, 1957 2,824,249 Hansen Feb. 18, 1958 2,843,799 Hook et al. July l5, 1958 2,857,551 Hansen Oct. 21, 1958 2,873,398 Crost Feb. 10, 1959 2,887,597 Smith et al May 19, 1959 FOREIGN PATENTS 634,318 Great Britain Mar. 15, 1950 886,457 France July 5, 1943 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3.031597 April 24 1962 Dean W. Davis It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 6, line 33, strike out "display" and insert the Same before "tubes" in line 34, same column 6.

Signed and sealed this 4th day of September- 1962.

SEAL) kttest:

ERNEST w. swlDER DAVID L. LADD fleeting Uffcer Commissioner of Patents 

